1. Field of the Invention
The present invention relates to a stent tube adapted to be placed in a body cavity of a human subject so as to drain, for example, a body fluid.
2. Description of the Related Art
Published Unexamined Japanese Utility Model Application 1-152636, for example, discloses a stent tube (hereinafter referred to a drainage tube) adapted to be placed in a human body to provide a passage for draining a body fluid, etc. In general, this type of drainage tube is formed of, for example, a polyethylene tube and, therefore, a poor frictional resistance and separation are involved. Thus the tube is liable to be clogged.
The drainage tube of the aforementioned Utility Model Application has a fluorine-based resin layer formed on its inner surface. FIG. 10 shows a practical arrangement of that drainage tube.
That is, the drainage tube 1 has a double-layered structure comprising an outer tube 2 made of polyethylene tube and an inner tube 3 made of a fluorine-based resin layer. The forward end 4 of drainage tube 1 has a tapering section 5 which is decreased in diameter toward its forward edge. A pair of cut areas 7,7 are provided one at the forward end portion and one at the rear end portion of the drainage tube 1 such that the cut areas 7,7 are inclined gradually toward the end edges of the drainage tube to provide a pair of openable/closable side flaps 8,8 there.
The aforementioned tube structure involves various drawbacks. First, the inner tube 3 in the double-layered structure is made of a fluorine-based resin and is more rigid than the outer tube 2 made of polyethylene, thus making the drainage tube 1 rigid as a whole. As one solution to this problem, if the outer tube 2 is made thinner, then a resultant pair of side flaps on the outer tube 2 becomes thinner, thus prominently lowering the ability with which the side flaps 8 are anchored on the body cavity of a human subject.
When the drainage tube 1 is inserted into the human body cavity through a channel of an endoscope, the drainage tube 1 passes through a forceps-raising base section. At that time, the drainage tube, if a thinner tube is used as the inner tube 3, is bent at the location of the forceps-raising base section, causing the bending of the inner tube 3 and the consequent collapsing of the inner tube 3. The collapsing of that tube is more liable to occur at the cut areas 7 providing the side flaps 8.
Second, if an inner tube 3 made of a fluorine-based resin is formed inside an outer tube 2 made of polyethylene so as to secure the same inner and outer diameters as those of a single ordinary drainage tube, it follows that the thickness of the outer tube 2 is thinned by the extent that the inner tube 3 is provided. Further, a contrast medium is mixed in the outer tube 2 so that the outer tube 2 is observable by an X-ray, but, in this case, the contrast medium in the outer tube 2 does not adequately secure its purpose. If, on the other hand, a contrast medium is mixed in the inner tube 3 made of a fluorine-based resin, a greater frictional resistance is involved so that the drainage tube fails to serve its own purpose fully.
Third, it is very difficult to make cut areas, as side flaps, in a relatively thin, outer tube 2 only. In this case it is necessary to initially insert an inner tube 3 of a fluorine-based resin into an outer tube and fix it there so that cut areas are provided as side flaps, etc. Upon assembly of a drainage tube by inserting the inner tube 3 into the outer tube 2, buckling is liable to occur at the cut areas of the outer tube 2. As a result, the drainage tube is difficult to manufacture and cannot be manufactured at low costs.